Young´s Modulus Determination for Case-Hardened Materials

Abstract

The issue of strength analysis as well as foreknowledge of component and structure life is of interest at this time for new composite materials. New composite materials and alloys elastic response is often unknown, and standard methods for their determining can not be applied to, e.g. materials featuring surface gradient properties. 
 Elasticity modulus method of examination is based on stepwise removal of part of the material from the rod sample surface or application of a coating onto the sample surface. Each step is accompanied by measurement of the sample lateral dimensions, and density. To determine Young´s modulus, resonance frequencies of the sample subjected to forced longitudinal vibrations are measured using an ultrasonic device. The device principle of operation is based on excitation and tracking of the sample forced mechanical oscillations close to its own frequencies, measurement of resonance peak parameters followed by calculations of the Young´s modulus. To induce and track the forced oscillations in the sample, use is made of piezoelectric transducers attached to damped acoustic transmission rods, while the sample is fixed between pointed rod ends. This arrangement makes it possible to examine also Young´s modulus temperature dependences.
 Young´s modulus measurement results for case-hardened hard alloy are provided. It is shown that Young´s modulus of surface layers is lower than that of the base material, which is explained by formation of new compounds in the surface layers owing to chemical and diffusion reactions between an alloying element and alloy components. The doped layer extends to 0.45 mm. The results obtained can be used for strength calculations of case-hardened materials, estimation of cohesive and adhesive strength of individual layers of coatings, structure and other physical and mechanical properties of materials.